Method of fabricating surface-emission type light-emitting device, surface-emitting semiconductor laser, method of fabricating the same, optical module and optical transmission device

ABSTRACT

A method of fabricating a surface-emission type light-emitting device which emits light in a direction perpendicular to a semiconductor substrate, includes the following steps (a) to (e). (a) A step of forming a column-shaped section by etching at least a part of a multilayer film. (b) A step of forming a first resin layer so as to cover the column-shaped section. (c) A step of forming a second resin layer by changing the solubility of the first resin layer in a liquid. (d) A step of immersing, for a specific period of time, at least the column-shaped section and the second resin layer in a liquid in which the second resin layer dissolves, thereby removing the second resin layer at least in the area formed over the column-shaped section. (e) A step of forming an insulating layer by curing the second resin layer.

This is a Division of application Ser. No. 10/092,777 filed Mar. 8, 2002now U.S. Pat. No. 6,900,069. Japanese Patent Application No. 2001-66299,filed on Mar. 9, 2001, Japanese Patent Application No. 2001-70726, filedon Mar. 13, 2001, Japanese Patent Application No. 2002-60316, filed onMar. 6, 2002 and Japanese Patent Application No. 2002-60751, filed onMar. 6, 2002, are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method of fabricating asurface-emission type light-emitting device which emits light in adirection perpendicular to a substrate. The present invention alsorelates to a surface-emitting semiconductor laser fabricated by theabove fabrication method which has stable characteristics duringdriving, and a method of fabricating the same. Furthermore, the presentinvention relates to an optical module and an optical transmissiondevice using the surface-emitting semiconductor laser.

A surface-emission type light-emitting device represented by asurface-emitting semiconductor laser is a two-dimensionally integratablelight-emitting device. Therefore, application of the surface-emissiontype light-emitting device to a wide range of fields such as a lightsource for high-speed, large-capacity optical communications has beenexpected.

Parasitic capacitance of the device causes a problem when driving alight-emitting device at a high speed. In the case of a surface-emittingsemiconductor laser, current must be injected into an active layer fromthe surface of a substrate in order to drive the device. In order toprevent current from being injected into the active layer from sectionsother than a light-emitting section (section contributing to emission oflight), an insulating layer is generally formed in a region other thannear the light-emitting section. An electrode is formed on the surfaceof the substrate through the insulating layer. Therefore, a layerstructure consisting of the electrode, insulating layer, andsemiconductor is formed in the device. This layer structure causesparasitic capacitance to occur.

This parasitic capacitance is decreased by increasing the thickness ofthe insulating layer. Therefore, a method of filling the periphery ofthe light-emitting section with an insulating resin represented by apolyimide and using the resin as the insulating layer has been employed.A surface-emitting semiconductor laser having such a structure isdisclosed in “Technical Report of IEICE”, LQE98-141, 1999-2 published bythe Institute of Electronics, Information and Communication Engineers.

An example of a common surface-emitting semiconductor laser in which theperiphery of the light-emitting section is filled with a resin and amethod of fabricating the same is shown in FIGS. 17 to 19. In asurface-emitting semiconductor laser 500 shown in FIG. 17, an activelayer 105 is formed in a column-shaped section 110 and light is emittedfrom a light exit port 116 on the upper surface of the column-shapedsection 110. In order to drive the surface-emitting semiconductor laser500, an electrode 113 for injecting current into the active layer 105must be formed over the column-shaped section 110, as shown in FIG. 17.The periphery of the column-shaped section 110 may be filled with aninsulating resin layer 517 in order to decrease the parasiticcapacitance of the device, as shown in FIG. 17. When forming thesurface-emitting semiconductor laser 500 shown in FIG. 17, after fillingthe periphery of the column-shaped section 110 with a resin layer 517 a,the resin layer 517 a is removed in the area formed over thecolumn-shaped section 110, and an upper electrode 113 must be formed soas to be connected to the upper surface of the column-shaped section110. Therefore, after filling the periphery of the column-shaped section110 with the resin layer 517 a, a device 500 a is installed in apolishing machine 550 and the resin 517 a is polished using abrasives551 using a CMP process or the like before forming the upper electrode113, as shown in FIG. 19, whereby the resin layer 517 a is removed inthe area formed over the column-shaped section 110.

However, the method shown in FIG. 19 may cause the column-shaped section110 to be polished at the same time as the resin layer 517 a. In thiscase, the device may be damaged or characteristics of the device maydeteriorate. Moreover, the resin or abrasive removed by polishing mayadhere to the device, thereby causing characteristics of the device todeteriorate. Therefore, it is difficult to obtain a device having stablecharacteristics unless the electrode 113 is formed after cleaning theupper surface of the column-shaped section 110 using a thorough cleaningstep and dry etching step in combination in addition to the polishingstep. The addition of the cleaning step increases the number of steps,thereby increasing the fabrication cost.

BRIEF SUMMARY OF THE INVENTION

The present invention may provide a method of fabricating asurface-emission type light-emitting device capable of producing adevice having stable characteristics at a lower cost and at high yields.

The present invention may also provide a surface-emitting semiconductorlaser fabricated by the method of fabricating a surface-emission typelight-emitting device which has stable device characteristics duringdriving, and a method of fabricating the same.

Further, the present invention may provide an optical module and anoptical transmission device using the surface-emitting semiconductorlaser.

Method of Fabricating Surface-Emission Type Light-Emitting Device

(1) According to the first aspect of the present invention, there isprovided a method of fabricating a surface-emission type light-emittingdevice including a column-shaped section formed on a substrate whichfunctions as at least a part of a light-emitting device, which emitslight in a direction perpendicular to the substrate, comprising thefollowing steps (a) to (e):

(a) a step of forming a multilayer film including an active layer on thesubstrate, and etching at least a part of the multilayer film so as toform the column-shaped section,

(b) a step of forming a first resin layer so as to cover thecolumn-shaped section,

(c) a step of forming a second resin layer by changing a solubility ofthe first resin layer in a specific liquid,

(d) a step of immersing, for a specific period of time, at least thesecond resin layer in the specific liquid having characteristics whichcause the second resin layer to dissolve, so as to remove the secondresin layer at least in the area formed over the column-shaped section,and

(e) a step of forming an insulating layer which covers a side surface ofthe column-shaped section by curing the second resin layer.

According to this aspect, only the second resin layer can be removedwithout causing damage to the column-shaped section in the step (d) byimmersing at least the second resin layer in the liquid for a specificperiod of time and removing the second resin layer in the area formedover the column-shaped section. This enables a device having stablecharacteristics to be obtained. Moreover, the device can be fabricatedat a lower cost and at high yields.

In this case, the step (c) may change the solubility of the first resinlayer in the specific liquid by applying one of heat and light to thefirst resin layer. This enables the second resin layer to be formed byeasily changing the solubility of the first resin layer in the specificliquid by applying either heat or light to the first resin layer,thereby the second resin layer can be removed efficiently in the areaformed over the column-shaped section.

(2) According to the second aspect of the present invention, there isprovided a method of fabricating a surface-emission type light-emittingdevice including a column-shaped section formed on a substrate whichfunctions as at least a part of a light-emitting device, which emitslight in a direction perpendicular to the substrate, comprising thefollowing steps (a) to (e):

(a) a step of forming a multilayer film including an active layer on thesubstrate, and etching at least a part of the multilayer film so as toform the column-shaped section,

(b) a step of forming a first resin layer including a resin precursor soas to cover the column-shaped section,

(c) a step of forming a second resin layer by semi-curing the firstresin layer,

(d) a step of immersing, for a specific period of time, at least thesecond resin layer in a liquid in which the second resin layerdissolves, so as to remove the second resin layer at least in the areaformed over the column-shaped section, and

(e) a step of forming an insulating layer which covers a side surface ofthe column-shaped section by curing the second resin layer.

“Semi-curing” in the step (c) means changing solubility of the firstresin layer in the liquid used in the step (d). By the semi-curing, thefirst resin layer converts to the second resin layer. In other words,solubility in the liquid used in the step (d) differs between the firstand the second resin layers.

According to this aspect, effects and advantages the same as thoseobtained by the fabrication method described in the above (1) can beachieved. For example, in the case of forming the second resin layerhaving a lower solubility in the liquid than the first resin layer bysemi-curing the first resin layer in the step (c), since the dissolvingspeed of the second resin layer in the liquid can be decreased by thissemi-curing step, a margin during the removal step of the second resinlayer in the liquid can be increased.

(3) According to the third aspect of the present invention, there isprovided a method of fabricating a surface-emission type light-emittingdevice including a column-shaped section formed on a substrate whichfunctions as at least a part of a light-emitting device, which emitslight in a direction perpendicular to the substrate, comprising thefollowing steps (a) to (e):

(a) a step of forming a multilayer film including an active layer on thesubstrate, and etching at least a part of the multilayer film so as toform the column-shaped section,

(b) a step of forming a first resin layer including a resin precursorand a photosensitive component so as to cover the column-shaped section,

(c) a step of converting a part of the first resin layer into a secondresin layer by exposing the first resin layer for a specific period oftime,

(d) a step of immersing, for a specific period of time, at least thesecond resin layer in a liquid in which the second resin layerdissolves, so as to remove the second resin layer, and

(e) a step of forming an insulating layer which covers a side surface ofthe column-shaped section by curing the first resin layer.

According to this aspect, effects and advantages the same as thoseobtained by the fabrication method described in the above (1) can beachieved. In the step (c), a part of the first resin layer is convertedinto the second resin layer having a higher solubility in the liquidthan the first resin layer by exposing the first resin layer, forexample. Since the dissolving speed of the second resin layer in theliquid can be increased by this exposure step, only the second resinlayer can be removed efficiently.

Moreover, since the liquid has characteristics which cause the secondresin layer to dissolve, components of the second resin layer can beprevented from readhering to the column-shaped section.

In this case, the photosensitive component may have characteristicswhich changes solubility in the liquid by light irradiation.

The methods of fabricating a surface-emission type light-emitting devicedescribed in the above (1) to (3) may have any of the following features(4) to (10).

(4) The liquid may have characteristics which removes the second resinlayer. This means that the liquid gets into the joint section betweenthe second resin layer and the column-shaped section during the processin which the second resin layer dissolves in the liquid, thereby thesecond resin layer is removed. With this characteristics, the secondresin layer can be removed efficiently in the area formed over thecolumn-shaped section.(5) The column-shaped section may have a lower solubility in the liquidthan the second resin layer. With this configuration, a sufficientmargin can be produced relating to the period of time in which thecolumn-shaped section and the second resin layer are immersed in theliquid, so that stable fabrication can be performed. Also, since thecolumn-shaped section can be prevented from dissolving in the liquidbefore the second resin layer, effects on the characteristics of thedevice can be limited.(6) The resin precursor may be a polyimide resin precursor.(7) The insulating layer may be formed of a polyimide resin.(8) The liquid may be an alkaline solution. The alkaline solution usedherein is a common basic solution.(9) The method may further comprise a step of forming a monitoringsection which monitors the removal of the second resin layer near thecolumn-shaped section. With this configuration, whether or not thesecond resin layer is removed in the area formed over the column-shapedsection can be detected precisely. As a result, the second resin layercan be removed in the area formed over the column-shaped section withoutcausing damage to the column-shaped section.

In this case, the monitoring section may be formed in the samepatterning step as the column-shaped section in the step (a).

(10) The surface-emission type light-emitting device may be any of asurface-emitting semiconductor laser, an LED device, and a semiconductorlight amplification device.

In the case where the surface-emission type light-emitting device is asurface-emitting semiconductor laser, the column-shaped section maycomprise an active layer, and the surface-emission type light-emittingdevice may comprise a resonator formed of a semiconductor depositionincluding the column-shaped section at least in part.

In this case, the method may further comprise the following step (f).

(f) A step of forming electrodes which inject current into the activelayer.

In this case, the method may further comprise a step of cleaning theupper surface of the column-shaped section before the step (f). By thisstep, a device having more stable characteristics can be obtained.

Surface-Emitting Semiconductor Laser and Method of Fabricating the SameSurface-Emitting Semiconductor Laser

According to the fourth aspect of the present invention, there isprovided a surface-emitting semiconductor laser including a resonatorformed on a semiconductor substrate, which emits light in a directionperpendicular to the semiconductor substrate, comprising:

a column-shaped section which forms at least a part of the resonator,and

an insulating layer which covers a side surface of the column-shapedsection,

wherein the insulating layer comprises a filler.

The direction perpendicular to the semiconductor substrate is thedirection perpendicular to the surface of the semiconductor substrate onwhich the resonator is formed.

According to this aspect, since the insulating layer comprises a filler,characteristics of the insulating layer such as thermal conductivity anda coefficient of thermal expansion can be adjusted. As a result,excellent device characteristics can be obtained. The details aredescribed in “DETAILED DESCRIPTION OF THE EMBODIMENT.”

The surface-emitting semiconductor laser of this aspect may have any ofthe following features (1) to (7).

(1) The filler may be formed of a material having thermal conductivityhigher than that of a matrix material which forms the insulating layer.With this configuration, heat generated from the resonator when drivingthe surface-emitting laser moves to the insulating layer so as to bediffused quickly through the filler included in the insulating layer.Thus, a rise in temperature of the resonator can be decreased. As aresult, a decrease in characteristics of the device due to heat can beprevented, thereby the stable device characteristics can be maintained.(2) The filler may be formed of a material having a coefficient ofthermal expansion different from that of a matrix material which makesup the insulating layer. According to this feature, the filler includedin the insulating layer adjust the difference in coefficient of thermalexpansion between the semiconductor substrate and the insulating layer,thereby a strain between the semiconductor substrate and the insulatinglayer can be reduced. Specifically, the difference in coefficient ofthermal expansion between the semiconductor substrate and the matrixmaterial which makes up the insulating layer can be decreased by usingthe filler having a specific coefficient of thermal expansioncorresponding to the difference in coefficient of thermal expansionbetween the semiconductor substrate and the insulating layer. As aresult, a strain between the semiconductor substrate and the insulatinglayer can be reduced and, therefore, reliability of the device can bemaintained.(3) The insulating layer may be formed of a matrix material such as apolyimide resin. In the fabrication of the surface-emitting laser, afterforming the insulating layer which covers a side surface of thecolumn-shaped section, an annealing is performed when forming a pair ofelectrodes on the upper surface of the column-shaped section and theback surface of the semiconductor substrate (a surface of thesemiconductor substrate opposite to the surface on which the resonatoris formed). Therefore, it is necessary to form the insulating layerusing a resin which can withstand the annealing step. Also, it isnecessary to form the insulating layer using a resin which enables theinsulating layer to be formed flat. In order to satisfy theserequirements, the insulating layer may be formed using a polyimide resinas a matrix material. The polyimide resin is excellent in heatresistance and operationality.(4) The particle diameter of the filler may be smaller than thethickness of the insulating layer. This enables the entire area of thefiller to be covered with the insulating layer.(5) The filler may be formed of an insulating material. This enables theelectrodes formed around the resonator to be insulated reliably. Asexamples of the insulating material, aluminum nitride, aluminum oxide,silicon nitride, silicon oxide, and the like can be given. The fillerformed of at least one of the above materials as an essential elementmay be used.

In this case, the filler may be formed of diamond and aluminum nitridebecause of its excellent thermal conductivity and insulation properties.

(6) The filler may be formed using at least one of carbon allotropessuch as carbon and graphite, or aluminum, gold, silver, copper, tin,magnesium, nickel, and zinc as an essential component. Since thesematerials have high thermal conductivity, heat generated from theresonator can be quickly diffused to the outside of the device throughthe filler by using at least one of these materials as an essentialcomponent of the filler. In this manner, the characteristics of thedevice can be stabilized.(7) The filler may be formed of a metal particle having an insulatingfilm on a surface. This enables insulation properties of the filler tobe increased.

The surface-emitting semiconductor laser of this aspect may be appliedto an optical module. In this case, the optical module comprises theabove described surface-emitting semiconductor laser and an opticalwaveguide. This optical module may be applied to an optical transmissiondevice.

Method of Fabricating Surface-Emitting Semiconductor Laser

(1) According to the fifth aspect of the present invention, there isprovided a method of fabricating a surface-emitting semiconductor laserincluding a resonator formed on a semiconductor substrate, which emitslight in a direction perpendicular to the semiconductor substrate,comprising the following steps (a) and (b):

(a) a step of forming a multilayer film on the semiconductor substrate,and etching at least a part of the multilayer film so as to form acolumn-shaped section including at least an active layer, and

(b) a step of forming an insulating layer which comprises a filler andcovers a side surface of the column-shaped section.

According to this aspect, a surface-emitting semiconductor laser havingstable characteristics can be obtained.

(2) According to the sixth aspect of the present invention, there isprovided a method of fabricating a surface-emitting semiconductor laserincluding a resonator formed on a semiconductor substrate, which emitslight in a direction perpendicular to the semiconductor substrate,comprising the following steps (a) to (e):

(a) a step of forming a multilayer film on the semiconductor substrate,and etching at least a part of the multilayer film so as to form acolumn-shaped section including at least an active layer,

(b) a step of forming a first matrix applying layer including a fillerand a matrix precursor so as to cover the column-shaped section,

(c) a step of forming a second matrix applying layer including thefiller and a provisional matrix material by temporarily solidifying thematrix precursor which forms the first matrix applying layer,

(d) a step of immersing, for a specific period of time, at least thesecond matrix applying layer in a liquid in which the provisional matrixmaterial forming the second matrix applying layer dissolves, so as toremove the second matrix applying layer at least in the area formed overthe column-shaped section, and

(e) a step of forming an insulating layer which comprises the filler andcovers a side surface of the column-shaped section by temporarily curingthe provisional matrix material which forms the second matrix applyinglayer.

In the case of temporarily solidifying the matrix precursor in the step(c), the matrix precursor which forms the first matrix applying layer isconverted into a provisional matrix material by irradiating the matrixprecursor with energy such as heat or light, for example. In this case,the provisional matrix material obtained by the temporal solidificationhas solubility in the liquid used in the step (d) different from that ofthe matrix precursor.

According to this aspect, only the second matrix applying layer can beremoved without causing damage to the column-shaped section in the step(d) by immersing at least the second matrix applying layer in the liquidfor a specific period of time and removing the second matrix applyinglayer in the area formed over the column-shaped section. This enables adevice having stable characteristics to be obtained. Moreover, thedevice can be fabricated at a lower cost and at high yields.

The filler in an upper part of the second matrix applying layer areautomatically removed from the second matrix applying layer as the upperpart of the second matrix applying layer is removed. This enables theinsulating layer including the filler to be formed at a uniformthickness by a step almost the same as a commonly used step for buryingan insulating layer.

Moreover, since the liquid has characteristics in which the provisionalmatrix material which forms the second matrix applying layer dissolves,the removed provisional matrix material can be prevented from readheringto the column-shaped section.

In the methods of fabricating a surface-emitting semiconductor laserdescribed in the above (1) and (2), the insulating layer may be formedof a matrix material such as a polyimide resin.

The method of fabricating a surface-emitting semiconductor laserdescribed in the above (2) may have any of the following features (3) to(5).

(3) The column-shaped section may have a lower solubility in the liquidthan the provisional matrix material which forms the second matrixapplying layer. With this configuration, a sufficient margin can beproduced relating to the period of time in which the column-shapedsection and the second matrix applying layer are immersed in the liquid,so that stable fabrication can be performed. Also, since thecolumn-shaped section can be prevented from dissolving in the liquidbefore the second matrix applying layer, effects on the characteristicsof the device can be limited.(4) The filler may have a lower solubility in the liquid than theprovisional matrix material which forms the second matrix applyinglayer. This enables the filler to be prevented from dissolving in theliquid before the provisional matrix material which forms the secondmatrix applying layer. Therefore, the filler can be included in theresulting insulating layer.(5) The matrix precursor may be a polyimide resin precursor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a view schematically showing a cross section of asurface-emission type light-emitting device according to a firstembodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a fabricationstep of the surface-emission type light-emitting device shown in FIG. 1.

FIG. 3 is a cross-sectional view schematically showing a fabricationstep of the surface-emission type light-emitting device shown in FIG. 1.

FIG. 4 is a plan view schematically showing the fabrication step shownin FIG. 3.

FIG. 5 is a cross-sectional view schematically showing a fabricationstep of the surface-emission type light-emitting device shown in FIG. 1.

FIG. 6 is a cross-sectional view schematically showing anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 1.

FIG. 7 is a cross-sectional view schematically showing anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 1.

FIG. 8 is a cross-sectional view schematically showing yet anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 1.

FIG. 9 is a view schematically showing a cross section of asurface-emission type light-emitting device according to a secondembodiment of the present invention.

FIG. 10 is a cross-sectional view schematically showing a fabricationstep of the surface-emission type light-emitting device shown in FIG. 9.

FIG. 11 is a cross-sectional view schematically showing anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 9.

FIG. 12 is a cross-sectional view schematically showing anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 9.

FIG. 13 is a cross-sectional view schematically showing anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 9.

FIG. 14 is a cross-sectional view schematically showing yet anotherfabrication step of the surface-emission type light-emitting deviceshown in FIG. 9.

FIG. 15 is a view schematically showing a cross section of asurface-emission type light-emitting device according to a thirdembodiment of the present invention.

FIG. 16 is a plan view schematically showing the surface-emission typelight-emitting device shown in FIG. 15.

FIG. 17 is a view schematically showing a cross section of a commonsurface-emission type light-emitting device.

FIG. 18 is a cross-sectional view schematically showing a fabricationstep of the common surface-emission type light-emitting device shown inFIG. 17.

FIG. 19 is a cross-sectional view schematically showing anotherfabrication step of the common surface-emission type light-emittingdevice shown in FIG. 17.

FIG. 20 is a view schematically showing a cross section of asurface-emission type light-emitting device (surface-emittingsemiconductor laser) according to a fourth embodiment of the presentinvention.

FIG. 21 is a cross-sectional view schematically showing a fabricationstep of the surface-emitting semiconductor laser shown in FIG. 20.

FIG. 22 is a cross-sectional view schematically showing anotherfabrication step of the surface-emitting semiconductor laser shown inFIG. 20.

FIG. 23 is a plan view schematically showing the fabrication step shownin FIG. 22.

FIG. 24 is a cross-sectional view schematically showing anotherfabrication step of the surface-emitting semiconductor laser shown inFIG. 20.

FIG. 25 is a cross-sectional view schematically showing anotherfabrication step of the surface-emitting semiconductor laser shown inFIG. 20.

FIG. 26 is a cross-sectional view schematically showing anotherfabrication step of the surface-emitting semiconductor laser shown inFIG. 20.

FIG. 27 is a cross-sectional view schematically showing yet anotherfabrication step of the surface-emitting semiconductor laser shown inFIG. 20.

FIG. 28 is a view illustrating a method of fabricating an optical moduleaccording to a fifth embodiment to which the present invention isapplied.

FIG. 29 is a view showing an optical transmission device according to asixth embodiment to which the present invention is applied.

FIG. 30 is a view showing the optical transmission device according tothe sixth embodiment to which the present invention is applied.

FIG. 31 is a view showing conditions of use of the optical transmissiondevice according to the sixth embodiment to which the present inventionis applied.

FIG. 32 is a view showing conditions of use of an optical transmissiondevice according to a seventh embodiment to which the present inventionis applied.

DETAILED DESCRIPTION OF THE EMBODIMENT

Embodiments of the present invention are described below with referenceto the drawings.

First Embodiment

Device Structure

FIG. 1 is a view schematically showing a cross section of asurface-emission type light-emitting device 100 according to a firstembodiment of the present invention.

The present embodiment illustrates a case where the surface-emissiontype light-emitting device 100 is a surface-emitting semiconductorlaser. In the surface-emission type light-emitting device 100, aninsulating layer 117 is formed on a vertical resonator (hereinaftercalled “resonator”) 120. The surface-emission type light-emitting device100 includes a semiconductor substrate 101, a buffer layer 102 formed ofn-type GaAs on the semiconductor substrate 101, the resonator 120, and acontact layer 108 formed of p-type GaAs on the resonator 120.

A column-shaped semiconductor deposition (column-shaped section) 110 isformed in the resonator 120. The column-shaped section 110, which ispart of the resonator 120, is a column-shaped semiconductor depositionincluding at least an active layer 105. The column-shaped section 110 isburied in the insulating layer 117. The side surface of thecolumn-shaped section 110 is covered with the insulating layer 117. Anupper electrode 113 is formed over the column-shaped section 110.

The resonator 120 includes a distributed-reflection type multilayer filmmirror 103 formed on the buffer layer 102 in which 30 pairs of n-typeAl_(0.85)Ga_(0.15)As layer and an n-type Al_(0.15)Ga_(0.85)As layer arelayered alternately (hereinafter called “lower mirror”), an n-typecladding layer 104 formed of n-type Al_(0.5)Ga_(0.5)As, the active layer105 formed of GaAs well layers and Al_(0.3)Ga_(0.7)As barrier layershaving a multiple quantum well structure in which the well layers areformed of three layers, a p-type cladding layer 106 formed ofAl_(0.5)Ga_(0.5)As, and a distributed-reflection type multilayer filmmirror 107 in which 25 pairs of a p-type Al_(0.85)Ga_(0.15)As layer anda p-type Al_(0.15)Ga_(0.85)As layer are layered alternately (hereinaftercalled “upper mirror”). These layers are applied in that order.

The upper mirror 107 is made p-type by Zn doping, and the lower mirror103 is made n-type by Se doping. Therefore, the upper mirror 107,undoped active layer 105, and lower mirror 103 make up a pin diode.

The resonator 120 is etched from the light exit side of thesurface-emission type light-emitting device 100 to the middle of thelower mirror 103 in the shape of a circle when viewed from the lightexit side, whereby a column-shaped section 110 is formed. In the presentembodiment, the planar shape of the column-shaped section 110 is acircle. However, the column-shaped section 110 may have a differentplanar shape.

In the surface-emission type light-emitting device 100 according to thepresent embodiment, the insulating layer 117 is formed to cover the sidesurface of the column-shaped section 110 and the upper surface of thelower mirror 103.

As a material for forming the insulating layer 117, resins formed bycuring by applying energy such as heat or light, such as a polyimideresin, acrylic resin, or epoxy resin may be used.

The upper electrode 113 is formed over the column-shaped section 110 andthe insulating layer 117. An opening 116, which becomes a laser exitport, is formed at the center of the upper surface of the column-shapedsection 110. A lower electrode 115 is formed on the surface of thesemiconductor substrate 101 opposite to the surface on which theresonator 120 is formed. Specifically, in the surface-emission typelight-emitting device 100 shown in FIG. 1, the upper electrode 113 isbonded to the column-shaped section 110, and the lower electrode 115 isbonded to the surface of the semiconductor substrate 101 opposite to thesurface on which the resonator 120 is formed. Current is injected intothe active layer 105 using the upper electrode 113 and the lowerelectrode 115.

Device Operation

The operation of the surface-emission type light-emitting device 100according to the first embodiment is described below. Thesurface-emission type light-emitting device 100 is a surface-emittingsemiconductor laser which emits laser light from the opening 116.

When a forward voltage is applied to the pin diode using the upperelectrode 113 and the lower electrode 115, electrons and holes arerecombined in the active layer 105, thereby causing emission of light tooccur. Stimulated emission occurs during a period in which the lightreciprocates between the upper mirror 107 and the lower mirror 103,whereby the intensity of light is amplified. Laser oscillation occurswhen the optical gain exceeds the optical loss, whereby laser light isemitted from the opening 116 formed in the upper electrode 113 in thedirection perpendicular to the semiconductor substrate 101.

Device Fabrication Process

A method of fabricating the surface-emission type light-emitting device100 according to the present embodiment is described below withreference to FIGS. 2 to 8. FIGS. 2, 3, and 5 to 8 are cross-sectionalviews schematically showing steps of fabricating the surface-emissiontype light-emitting device of the present embodiment. FIG. 4 is a planview schematically showing the fabrication step shown in FIG. 3.

The surface-emission type light-emitting device 100 of the presentembodiment is fabricated by the following steps (a) to (e).

The step (a) includes forming a multilayer film including the activelayer 105 on the semiconductor substrate 101, and etching at least apart of the multilayer film, thereby forming the column-shaped section110 which functions as at least a part of the light-emitting device 100.

The step (b) includes forming a first resin layer 117 a so as to coverthe column-shaped section 110.

The step (c) includes forming a second resin layer 117 b by changing thesolubility of the first resin layer 117 a in a liquid 130 (describedlater).

The step (d) includes immersing, for a specific period of time, at leastthe second resin layer 117 b in the liquid 130 having characteristicswhich cause the second resin layer 117 b to be dissolved, therebyremoving the second resin layer 117 b at least in the area formed overthe column-shaped section 110.

The step (e) includes forming the insulating layer 117 which covers theside surface of the column-shaped section 110 by curing a second resinlayer 117 c.

The step (a) is described below.

The semiconductor multilayer film 150 shown in FIG. 2 is epitaxiallygrown on the surface of the n-type GaAs semiconductor substrate 101shown in FIG. 2 while changing the composition. The semiconductormultilayer film 150 includes the buffer layer 102 formed of n-type GaAs,the lower mirror 103 in which n-type Al_(0.85)Ga_(0.15)As layers andn-type Al_(0.15)Ga_(0.85)As layers are applied alternately, the n-typecladding layer 104 formed of n-type Al_(0.5)Ga_(0.5)As, the active layer105 formed of GaAs well layers and Al_(0.3)Ga_(0.7)As barrier layershaving a multiple quantum well structure in which the well layers areformed of three layers, the p-type cladding layer 106 formed ofAl_(0.5)Ga_(0.5)As, the upper mirror 107 in which p-typeAl_(0.85)Ga_(0.15)As layers and p-type Al_(0.15)Ga_(0.85)As layers areapplied alternately, and the contact layer 108 formed of p-type GaAs.The semiconductor multilayer film 150 is formed by depositing theselayers on the semiconductor substrate 101 in that order. The surface ofthe semiconductor substrate 101 is the surface on which the resonator120 is formed in the steps described later.

The epitaxial growth temperature is appropriately determined accordingto the type of the semiconductor substrate 101 or the type or thicknessof the semiconductor multilayer film 150. The epitaxial growthtemperature is preferably 600 to 800° C. A period of time needed for theepitaxial growth is also appropriately determined. As the epitaxialgrowth method, an Metal-Organic Vapor Phase Epitaxy (MOVPE) method,Molecular Beam Epitaxy (MBE) method, or Liquid Phase Epitaxy (LPE)method may be used.

A photoresist (not shown) is applied to the contact layer 108 andpatterned using photolithography, thereby forming a resist layer (notshown) with a specific pattern. Part of the contact layer 108, uppermirror 107, p-type cladding layer 106, active layer 105, n-type claddinglayer 104, and lower mirror 103 is dry-etched using the resist layer asa mask, thereby forming the column-shaped section 110 which is acolumn-shaped semiconductor deposition, as shown in FIGS. 3 and 4. Theresonator 120 including the column-shaped section 110 is formed on thesemiconductor substrate 101 by this step.

The step (b) is described below.

In this step, the column-shaped section 110 is covered with the firstresin layer 117 a.

A liquid substance containing a resin precursor (not shown) is appliedto the column-shaped section 110 and the upper mirror 103 and thendried, thereby forming the first resin layer 117 a so as to cover thecolumn-shaped section 110, as shown in FIG. 5. In this step, the firstresin layer 117 a is formed so that the thickness of the first resinlayer 117 a is greater than at least the height of the column-shapedsection 110, and the column-shaped section 110 is covered with the firstresin layer 117 a. The resin precursor is applied after dissolving in asolvent, as required. In this case, the solvent is evaporated afterapplying the resin precursor.

As a method of applying the liquid substance, conventional techniquesuch as a spin coating process, dipping process, or spray coatingprocess may be used. During the application, it is preferable to preventunevenness of the film thickness caused by a convex section formed bythe column-shaped section 110 as far as possible.

The step (c) is described below.

In this step, the resin precursor in the first resin layer 117 a issemi-cured by applying energy such as heat or light to the resinprecursor, thereby forming the second resin layer 117 b, as shown inFIG. 6. The semi-curing in the step (c) means changing solubility of thefirst resin layer 117 a in the liquid 130 described later. By thesemi-curing, the first resin layer 117 a converts to the second resinlayer 117 b. In other words, solubility in the liquid 130 differsbetween the first resin layer 117 a and the second resin layer 117 b. Inthe present embodiment, part of the resin precursor in the first resinlayer 117 a is reacted by applying energy such as heat or light, wherebythe second resin layer 117 b having a lower solubility in the liquid 130than the first resin layer 117 a is formed.

This semi-curing step is performed while controlling the period of timefor applying energy such as heat or light and the amount of energy to beapplied depending on the type of the resin precursor in the first resinlayer 117 a. In the case of semi-curing the resin precursor using heat,the reaction temperature is controlled. In the case of semi-curing theresin precursor using light, the amount of light is controlled. In thecase of forming the second resin layer 117 b having a lower solubilityin the liquid 130 than the first resin layer 117 a by semi-curing thefirst resin layer 117 a using heat, the semi-curing is performed at atemperature lower than that employed in a heat curing step for formingan insulating layer from the first resin layer 117 a. If the amount ofenergy applied is insufficient, the solubility in the liquid 130 is notsufficiently changed, thereby the resin layer dissolves in the liquid130 and the resin layer is almost removed. If the amount of energyapplied is too great, the solubility in the liquid 130 becomes too low,whereby it is difficult to remove the second resin layer 117 b in thestep described later. Therefore, it is important to control the amountof energy to be applied and the period of time during semi-curingdepending on the type of the resin precursor.

As an example of the resin precursor used in this step, a polyimideprecursor can be given.

As examples of the polyimide precursor, polyamic acid, long-chain alkylester of polyamic acid, and the like can be given. In the case offorming the insulating layer from the polyimide precursor, when thepolyimide precursor is applied and then heated, an imidization reactionoccurs. As a result, a polyimide resin is produced, whereby theinsulating layer is formed. The heating temperature applied when formingthe insulating layer is suitably 250 to 400° C., although thetemperature is changed depending on the type of the polyimide precursor.In this case, the semi-curing step is preferably performed at 150 to250° C.

In the case of using a resin cured by light irradiation as the resinused for forming the insulating layer 117 (see FIG. 1), a UV-curablepolyacrylic resin or epoxy resin may be used. Since the UV-curable resincan be cured by only irradiation with ultraviolet rays, problems such aschanges in the device characteristics due to heat can be avoided.

The step (d) is described below.

In this step, a device 100 a obtained by the above steps is immersed inthe liquid 130 for a specific period of time, as shown in FIG. 7. FIG. 7illustrates a case where the entire area of the device 100 a is immersedin the liquid 130. However, it suffices that at least the second resinlayer 117 b of the device 100 a be immersed.

The liquid 130 has characteristics which cause the second resin layer117 b to be dissolved. The liquid 130 may be appropriately selectedcorresponding to the characteristics of the resin precursor. Forexample, a resin precursor having solubility in an alkaline solution maybe selected as the resin precursor. In this case, an alkaline solutionmay be used as the liquid 130.

The liquid 130 preferably has characteristics which cause the secondresin layer 117 b to be removed. This means that the liquid 130 isintroduced into the joint section between the second resin layer 117 band the column-shaped section 110 during the process in which the secondresin layer 117 is dissolved in the liquid 130, whereby the second resinlayer 117 is removed. If the liquid 130 has characteristics which causethe second resin layer 117 b to be removed, the second resin layer 117 bcan be removed efficiently in the area formed over the column-shapedsection 110.

In this step, the solubility of the column-shaped section 110 in theliquid 130 may be lower than the solubility of the second insulatinglayer 117 b in the liquid 130. This enables a sufficient margin to beproduced relating to the period of time in which the column-shapedsection 110 and the second resin layer 117 b are immersed in the liquid130, thereby enabling stable fabrication. Moreover, since thecolumn-shaped section 110 can be prevented from being dissolved in theliquid 130 before the second resin layer 117 b, effects on the devicecharacteristics can be limited.

In this step, a second insulating layer 117 c is obtained by controllingthe period of time and temperature for immersion in the liquid 130, asshown in FIG. 8. The second insulating layer 117 c is formed of thesecond resin layer 117 b shown in FIG. 7 of which the area formed overthe column-shaped section 110 is removed, as shown in FIG. 8. In thisstep, the area of the second resin layer 117 b formed over the uppermirror 103 is also dissolved in the liquid 130. As a result, the secondinsulating layer 117 c can be formed so that the upper surface of thesecond insulating layer 117 c is almost level with the upper surface ofthe column-shaped section 110.

The step (e) is described below.

In this step, the insulating layer 117 which covers the side surface ofthe column-shaped section 110 is formed by curing the second resin layer117 c. The second resin layer 117 c is cured at a temperature for aperiod of time referring to the temperature and period of time in aconventional curing step during formation of an insulating layer. Theinsulating layer 117 which covers the side surface of the column-shapedsection 110 is formed by this step, as shown in FIG. 1.

A step of forming the electrodes 113 and 115 for injecting current intothe active layer 105 (step (f)) is described below.

Before forming the electrodes 113 and 115, the upper surface of thecolumn-shaped section 110 is optionally cleaned using a dry etchingprocess or the like. This enables formation of a device having morestable characteristics. After forming an alloy layer of gold or zinc onthe upper surfaces of the insulating layer 117 and the column-shapedsection 110 using a vacuum deposition process, the alloy layer ispatterned using photolithography, thereby forming the opening 116. Theupper electrode 113 is formed by this step. The lower electrode 115 isformed of a gold/germanium alloy layer on the back surface of thesemiconductor substrate 101 (surface of the semiconductor substrate 101opposite to the surface on which the resonator 120 is formed) using avacuum deposition process. The surface-emission type light-emittingdevice 100 shown in FIG. 1 is obtained by the above process.

Action and Effects

The action and effects of the first embodiment are described below.

According to the method of fabricating the surface-emission typelight-emitting device 100 of the present embodiment, the second resinlayer 117 b can be removed in the area formed over the column-shapedsection 110 without causing damage to the column-shaped section 110 inthe step (d) by immersing at least the second resin layer 117 b in theliquid 130. This enables the device 100 having stable characteristics tobe obtained. Moreover, the device 100 can be fabricated at a lower costand at high yields. Since the greater part of the removed second resinlayer 117 b is dissolved in the liquid 130, the device characteristicsscarcely deteriorate due to the second resin layer 117 b readhering tothe device 100 after removal.

In the step (c), the second resin layer 117 b having a lower solubilityin the liquid 130 than the first resin layer 117 a is formed bysemi-curing the first resin layer 117 a. Since the dissolving rate ofthe second resin layer 117 b in the liquid 130 can be decreased by thissemi-curing step, a margin during the removal step of the second resinlayer 117 b in the liquid 130 can be increased.

Second Embodiment

Device Structure

FIG. 9 is a view schematically showing a cross section of asurface-emission type light-emitting device 200 according to a secondembodiment of the present invention.

In the surface-emission type light-emitting device 200 according to thepresent embodiment, the side surface of the column-shaped section 110 iscovered with an insulating layer 217. The insulating layer 217 is formedof a first insulating layer 217 a (see FIG. 10) containing resinprecursor and photosensitive components. The surface-emission typelight-emitting device 200 of the present embodiment differs from thesurface-emission type light-emitting device 100 of the first embodimentwhich includes the insulating layer 117 relating to this point. Thestructure of other sections of the surface-emission type light-emittingdevice 200 is the same as that of the surface-emission typelight-emitting device 100 of the first embodiment. Therefore, furtherdescription of these sections is omitted.

Device Operation

The operation of the surface-emission type light-emitting device 200 ofthe second embodiment is the same as that of the surface-emission typelight-emitting device 100 of the first embodiment. Therefore, furtherdescription is omitted.

Device Fabrication Process

A method of fabricating the surface-emission type light-emitting device200 of the present embodiment is described below with reference to FIGS.2 to 4 and FIGS. 10 to 14. FIGS. 2 to 4 and FIGS. 10 to 14 arecross-sectional views schematically showing steps of fabricating thesurface-emission type light-emitting device 200 of the presentembodiment.

The surface-emission type light-emitting device 200 of the presentembodiment is fabricated by the following steps (a) to (e).

The step (a) includes forming a multilayer film including the activelayer 105 on the semiconductor substrate 101, and etching at least apart of the multilayer film, thereby forming the column-shaped section110 which functions as at least a part of the light-emitting device 200.

The step (b) includes forming a first resin layer 217 a so as to coverthe column-shaped section 110.

The step (c) includes converting a part of the first resin layer 217 ainto a second resin layer 217 b by exposing the first resin layer 217 afor a specific period of time.

The step (d) includes immersing, for a specific period of time, at leastthe second resin layer 217 b in a liquid 230 having characteristicswhich cause the second resin layer 217 b to be dissolved, therebyremoving the second resin layer 217 b.

The step (e) includes forming an insulating layer 217 which covers theside surface of the column-shaped section 110 by curing the second resinlayer 217 b.

The step (a) is described below.

As shown in FIGS. 2 to 4, the semiconductor multilayer film 150 isformed on the semiconductor substrate 101, and the resonator 120including the column-shaped section 110 is formed on the semiconductorsubstrate 101, in the same manner as in the step (a) of fabricating thesurface-emission type light-emitting device 100 of the first embodiment.The step (a) is almost the same as the fabrication step (a) in the firstembodiment. Therefore, detailed description is omitted.

The step (b) is described below.

The step (b) includes forming the first resin layer 217 a to cover thecolumn-shaped section 110. In this step, the column-shaped section 110is covered with the first resin layer 217 a.

A liquid substance (not shown) containing a resin precursor andphotosensitive components is applied to the column-shaped section 110and the upper mirror 103 and then dried, thereby forming the first resinlayer 217 a so as to cover the column-shaped section 110, as shown inFIG. 10. In this step, the first resin layer 217 a is formed so that thethickness of the first resin layer 217 a is at least greater than theheight of the column-shaped section 110, and the column-shaped section110 is covered with the first resin layer 217 a. The liquid substance isapplied after dissolving in a solvent, as required. In this case, thesolvent is evaporated after the liquid substance is applied. As a methodof applying the liquid substance, methods the same as the methods ofapplying the resin precursor illustrated in the first embodiment may beused.

The step (c) is described below.

This step includes converting a part of the first resin layer 217 a intothe second resin layer 217 b by exposing the first resin layer 217 a, asshown in FIG. 11. In the present embodiment, the area of the first resinlayer 217 a formed higher than the upper surface of the column-shapedsection 110 is converted into the second resin layer 217 b by adjustingthe dose of exposure, as shown in FIG. 12. A device 200 a is obtained bythis step. In the device 200 a, the side surface of the column-shapedsection 110 is covered with the first resin layer 217 a, and the secondresin layer 217 b is formed on the first resin layer 217 a and thecolumn-shaped section 110.

The second resin layer 217 b is the first resin layer 217 a of which thesolubility in the liquid 230 is changed as a result of the reaction ofat least a part of the photosensitive components in the first resinlayer 217 a by exposure. The photosensitive components included in thefirst resin layer 217 a have characteristics by which the solubility inthe liquid 230 (see FIG. 12) described later is increased by changes instructure due to reaction by exposure. Specifically, the second resinlayer 217 b has a higher solubility in the liquid 230 than the firstresin layer 217 a.

This exposure step is performed while controlling the exposure time andexposure dose depending on the type and density of the photosensitivecomponents included in the first resin layer 217 a. In the presentembodiment, in the case where a part of the first resin layer 217 a isconverted into the second resin layer 217 b by exposure, the first resinlayer 217 a is exposed at a dose smaller than that used in the exposurestep for forming a common insulating layer from the first resin layer217 a, or the first resin layer 217 a is exposed for a period of timeshorter than that employed in the exposure step for forming a commoninsulating layer from the first resin layer 217 a. In the case ofconverting a part of the first resin layer 217 a into the second resinlayer 217 b having a higher solubility in the liquid 230 than the firstresin layer 217 a by exposing the first resin layer 217 a to light, ifthe dose of exposing light is insufficient, solubility of the resinlayer for the liquid 230 is not increased. As a result, the resin layeris scarcely dissolved in the liquid 230, whereby it is difficult toremove the resin layer in the succeeding step. If the dose of exposinglight is too great, the entire area of the first resin layer 217 a isconverted into the second resin layer 217 b having a higher solubilityin the liquid 230, whereby the entire resin layer is dissolved whenimmersed in the liquid 230. Therefore, it is important to control theexposure time and dose during exposure depending on the type of thephotosensitive components.

As an example of the resin precursor used in this step, a positive-tonephotosensitive polyimide precursor can be given.

The step (d) is described below.

In this step, the device 200 a obtained by the above steps is immersedin the liquid 230 for a specific period of time, as shown in FIG. 13.FIG. 13 illustrates a case where the entire area of the device 200 a isimmersed in the liquid 230. However, it suffices that the second resinlayer 217 b of the device 200 a be immersed in the liquid 230.

The liquid 230 has characteristics which cause the second resin layer217 b to be dissolved. The liquid 230 may be appropriately selectedcorresponding to the characteristics of the resin precursor and thephotosensitive components which make up the second resin layer 217 b.

The liquid 230 may have characteristics which cause the second resinlayer 217 b to be removed. This enables effects the same as by theliquid 130 to be achieved.

In this step, the solubility of the column-shaped section 110 in theliquid 230 may be lower than the solubility of the second insulatinglayer 217 b in the liquid 230. This enables effects the same as by theliquid 130 to be achieved.

In this step, the second insulating layer 217 b shown in FIG. 13 isremoved by controlling the period of time and temperature for immersionin the liquid 230 in the same manner as in the device of the firstembodiment shown in FIG. 8. As a result, the first resin layer 217 awhich covers the side surface of the column-shaped section 110 and formsalmost the same plane as the upper surface of the column-shaped section110 is obtained. The insulating layer 217 which covers the side surfaceof the column-shaped section 110 is formed by curing the firstinsulating layer 217 a using the same method as the method of curing thesecond resin layer 117 c in the step of fabricating the surface-emissiontype light-emitting device 100 of the first embodiment, as shown in FIG.9.

The succeeding steps are the same as those of the steps of fabricatingthe surface-emission type light-emitting device 100 of the firstembodiment. Therefore, description of these steps is omitted. Thesurface-emission type light-emitting device 200 shown in FIG. 9 isobtained by the above process.

Action and Effects

The action and effects of the second embodiment are described below.

According to the method of fabricating the surface-emission typelight-emitting device 200 of the second embodiment, only the secondresin layer 217 b can be removed without causing damage to thecolumn-shaped section 110 by immersing the second resin layer 217 b inthe liquid 230 for a specific period of time and removing the secondresin layer 217 b. This enables the device 200 having stablecharacteristics to be obtained in the same manner as thesurface-emission type light-emitting device 100 of the first embodiment.Moreover, the device 200 can be fabricated at a lower cost and at highyields. Since the greater part of the removed second resin layer 217 bis dissolved in the liquid 230, the device characteristics scarcelydeteriorate due to the second resin layer 217 b readhering to the device200 after removal.

In the step (c), a part of the first resin layer 217 a is converted intothe second resin layer 217 b having a lower solubility in the liquid 230than the first resin layer 217 a by exposing the first resin layer 217a. Since the dissolving rate of the second resin layer 217 b in theliquid 230 can be increased by this exposure step, only the second resinlayer 217 b can be removed efficiently.

The surface-emission type light-emitting device 200 of the secondembodiment and the method of fabricating the same have the same effectsand advantages as the surface-emission type light-emitting device 100 ofthe first embodiment and the method of fabricating the same.

Third Embodiment

Device Structure

FIG. 15 is a view schematically showing a cross section of asurface-emission type light-emitting device 300 according to a thirdembodiment of the present invention. FIG. 16 is a plan viewschematically showing the surface-emission type light-emitting device300 shown in FIG. 15.

The surface-emission type light-emitting device 300 of the presentembodiment includes a monitoring section 320 formed near thecolumn-shaped section 110, as shown in FIGS. 15 and 16, in addition tothe same structure as the surface-emission type light-emitting device100 of the first embodiment. The monitoring section 320 is formed by thesame patterning step as the column-shaped section 110. In thefabrication step of the surface-emission type light-emitting device 300,the insulating layer 117 shown in FIG. 17 is formed in the same step asthe surface-emission type light-emitting device 100 of the firstembodiment. Specifically, the second resin layer 117 b is removed in thearea formed over the column-shaped section 110 by immersing at least thesecond resin layer 117 b in the liquid 130 (see FIG. 8) for a specificperiod of time, whereby the insulating layer 117 is formed.

The monitoring section 320 is provided to monitor the degree of removalof the second resin layer 117 b in the step of removing the second resinlayer 117 b from the area formed over the column-shaped section 110 byimmersing at least the second resin layer 117 b in the liquid 130 for aspecific period of time. For example, the reflectance on the uppersurface of the monitoring section 320 is changed when the second resinlayer 117 b is removed in the area present on the upper surface of themonitoring section 320 in the case of immersing the monitoring section320, the column-shaped section 110 and the second resin layer 117 b inthe liquid 130. The degree of removal of the second resin layer 117 bcan be confirmed by measuring the changes in reflectance on the uppersurface of the monitoring section 320. This enables the removal of thesecond resin layer 117 b formed over the column-shaped section 110 to becontrolled.

The planar shape of the monitoring section 320 is preferablyrectangular. The ratio of the long side to the short side of thisrectangle is preferably greater. This enables the conditions under whichthe second resin layer 117 b is removed in the area present on the uppersurface of the monitoring section 320 in the liquid 130 to be detectedprecisely.

Device Fabrication Process

The surface-emission type light-emitting device 300 of the presentembodiment is fabricated essentially by the same steps as thesurface-emission type light-emitting device 100 of the first embodimentexcept that the monitoring section 320 is formed by the same step as thestep of forming the column-shaped section 110 by patterning.Specifically, in the fabrication steps of the surface-emission typelight-emitting device 100 of the first embodiment, the monitoringsection 320 is formed at the same time as the column-shaped section 110by the patterning step shown in FIGS. 3 and 4. Since other steps are thesame as the steps for fabricating the surface-emission typelight-emitting device 100, description of these steps is omitted.

Device Operation

The operation of the surface-emission type light-emitting device 300 ofthe present embodiment is the same as that of the surface-emission typelight-emitting devices 100 and 200 of the first and the secondembodiments. Therefore, description thereof is omitted.

Action and Effects

The action and effects of the surface-emission type light-emittingdevice 300 of the present embodiment and the method of fabricating thesame are almost the same as those of the surface-emission typelight-emitting device 100 of the first embodiment and the method offabricating of the same. The third embodiment has the followingadditional action and effects.

Since the monitoring section 320 is formed near the column-shapedsection 110, the removal or non-removal of the second resin layer 117 bin the area formed over the column-shaped section 110 can be detected.As a result, the second resin layer 117 b can be removed more reliablyin the area formed over the column-shaped section 110 without causingdamage to the column-shaped section 110. This enables the device 300having stable characteristics to be fabricated at high yields.

In the first to third embodiments, the p-type and n-type layers in eachsemiconductor layer may be replaced by the n-type and p-type layers,respectively. Such a modification is within the scope of the presentinvention. The above embodiments illustrate the case of using AlGaAsmaterials. Other materials such as GaInP, ZnSSe, InGaN, or GaAsSbsemiconductor materials may be used depending on the oscillationwavelength.

The first to third embodiments illustrate the case where thesurface-emission type light-emitting device is a surface-emittingsemiconductor laser. However, the surface-emission type light-emittingdevice is not limited to the surface-emitting semiconductor laser. Thesurface-emission type light-emitting device is a light-emitting devicewhich emits light in the direction perpendicular to the substrate. Asthe surface-emission type light-emitting device applicable to thepresent invention, an LED device, a semiconductor light amplificationdevice, and the like can be given in addition to the surface-emittingsemiconductor laser.

The above method of driving the surface-emission type light-emittingdevice is only an example. Various modifications and variations arepossible within the scope of the present invention. The aboveembodiments illustrate the surface-emission type light-emitting devicehaving one column-shaped section. However, the present invention is notimpaired even if a plurality of column-shaped sections is provided onthe substrate.

Fourth Embodiment

Device Structure

FIG. 20 is a cross-sectional view schematically showing a cross sectionof a surface-emission type light-emitting device of the presentembodiment. The present embodiment illustrates a case where thesurface-emission type light-emitting device is a surface-emittingsemiconductor laser (hereinafter called “surface-emitting laser”) 400.

In the surface-emitting laser 400 of the present embodiment, theinsulating layer 417 is formed on the resonator 120. Thesurface-emitting laser 400 includes the semiconductor substrate 101formed of GaAs, the buffer layer 102 formed of n-type GaAs on thesemiconductor substrate 101, the resonator 120, and the contact layer108 formed of p-type GaAs on the resonator 120.

The column-shaped semiconductor deposition (column-shaped section) 110is formed in the resonator 120. The column-shaped section 110, which ispart of the resonator 120, is a column-shaped semiconductor depositionincluding at least the contact layer 108 and the upper mirror 107. Thecolumn-shaped section 110 is buried in the insulating layer 417.Specifically, the side surface of the column-shaped section 110 iscovered with the insulating layer 417. The upper electrode 113 is formedover the column-shaped section 110.

The resonator 120 includes the distributed-reflection type multilayerfilm mirror 103 formed on the buffer layer 102 in which 30 pairs of ann-type AlAs layer and an n-type Al_(0.15)Ga_(0.85)As layer are appliedalternately (hereinafter called “lower mirror”), the n-type claddinglayer 104 formed of n-type Al_(0.5)Ga_(0.5)As, the active layer 105formed of GaAs well layers and Al_(0.3)Ga_(0.7)As barrier layers havinga multiple quantum well structure in which the well layers are formed ofthree layers, the p-type cladding layer 106 formed ofAl_(0.5)Ga_(0.5)As, and the distributed-reflection type multilayer filmmirror 107 in which 25 pairs of a p-type Al_(0.85)Ga_(0.15)As layer anda p-type Al_(0.15)Ga_(0.85)As layer are applied alternately (hereinaftercalled “upper mirror”). These layers are formed in that order.

The upper mirror 107 is made p-type by Zn doping, and the lower mirror103 is made n-type by Si doping. Therefore, the upper mirror 107,undoped active layer 105, and lower mirror 103 make up a pin diode.

The resonator 120 is etched from the light exit side of thesurface-emitting laser 400 to the middle of the lower mirror 103 in theshape of a circle when viewed from the light exit side, whereby thecolumn-shaped section 110 is formed. In the present embodiment, theplanar shape of the column-shaped section 110 is a circle. However, thecolumn-shaped section 110 may have a different planer shape.

In the surface-emitting laser 400 according to the present embodiment,the insulating layer 417 is formed to cover the side surface of thecolumn-shaped section 110 and the upper surface of the lower mirror 103.

The insulating layer 417 is formed of a matrix material in which fillers160 are mixed. The present embodiment illustrates a case in which thematrix material forming the insulating layer 417 is a resin 163 (seeFIG. 20). The resin 163 is formed by curing by irradiation with energysuch as heat or light or by a chemical reaction.

In the fabrication of the surface-emitting laser 400, after forming theinsulating layer 417 which covers the side surface of the column-shapedsection 110, an annealing step for forming the electrodes 113 and 115respectively on the upper surface of the column-shaped section 110 andthe back surface of the semiconductor substrate 101 (the surface of thesemiconductor substrate 101 opposite to the surface on which theresonator 120 is formed) is performed at about 400° C. (refer tofabrication process described later). Therefore, the matrix material(resin 163 in the present embodiment) which forms the insulating layer417 must excel in heat resistance to withstand this annealing step.Since the column-shaped section 110 is generally formed at a height ofabout 3 μm or more, the resin 163 which forms the insulating layer 417must be formed flat with a thickness of at least about 3 μm. In order tosatisfy the above requirements, the resin 163 is preferably a polyimideresin, acrylic resin, or epoxy resin, and particularly preferably apolyimide resin.

The insulating layer 417 includes the fillers 160, as shown in FIG. 20.FIG. 20 illustrates the case where the fillers 160 are spherical.However, the shape of the fillers 160 is not limited thereto. Thefillers 160 may be plate-shaped, fibrous, amorphous, hollow, or thelike. The size of the fillers 160 is not limited. It is preferable thatthe entire area of the fillers 160 be covered with the insulating layer417. Therefore, the particle diameter of the fillers 160 is preferablysmaller than the thickness of the insulating layer 417. The insulatinglayer 417 may be formed using a plurality of fillers having differentparticle diameters. This enables the filling density of the fillers 160in the insulating layer 417 to be increased.

The fillers 160 may be formed of a material having a thermalconductivity greater than that of the resin 163 which forms theinsulating layer 417. This ensures that heat generated from theresonator 120 at the time of driving the surface-emitting laser 400 andmoved to the insulating layer 417 is diffused immediately through thefillers 160 in the direction opposite to the column-shaped section 110.This prevents an increase in temperature of the resonator 110. As aresult, a decrease in characteristics of the device due to heat can beprevented, whereby stable characteristics can be maintained.

The fillers 160 may be formed of a material having a coefficient ofthermal expansion differing from that of the resin 163 which forms theinsulating layer 417. The reasons therefor are described later.

As the material for the fillers 160, silicon, carbon allotropes, metals,and the like may be used. As examples of carbon allotropes, diamond,graphite, carbon black, and the like can be given. As examples ofmetals, aluminum, gold, silver, copper, tin, magnesium, nickel, and zinccan be given. In the case using a metal for the fillers 160, a metalwith an insulating film such as an oxide film or nitride film formed onthe surface may be used. The insulating film formed on the surfaceincreases insulation properties of the fillers.

In the case where the fillers 160 contain at least one metal among theabove metals as an essential component, since these metals excel inthermal conductivity, heat generated from the resonator 120 can bequickly diffused to the outside through the fillers 160. This enablesstabilization of the characteristics of the device.

The fillers 160 may be formed of an insulating material. If the fillers160 are formed of an insulating material, the upper electrode 113 andthe lower electrode 115 can be insulated reliably. As examples of theinsulating material, diamond, carbon, silicon, aluminum nitride,aluminum oxide, silicon carbide (silicon nitride), silicon oxide,silicon nitride, boron carbide, and the like can be given. Inparticular, diamond and aluminum nitride is preferably used as thematerial for the fillers 160 because of its excellent thermalconductivity and insulation properties.

The upper electrode 113 is formed over the column-shaped section 110 andthe insulating layer 417. The opening 116, which becomes a laser exitport, is formed at the center of the upper surface of the column-shapedsection 110. The lower electrode 115 is formed on the back surface ofthe semiconductor substrate 101. Specifically, in the surface-emittinglaser 400 shown in FIG. 20, the upper electrode 113 is bonded to thecolumn-shaped section 110, and the lower electrode 115 is bonded to thesurface of the semiconductor substrate 101 opposite to the resonator120. Current is injected into the active layer 105 using the upperelectrode 113 and the lower electrode 115.

Device Operation

The operation of the surface-emitting laser 400 according to the fourthembodiment is described below. The method of driving thesurface-emitting semiconductor laser described below is only an example.Various modifications and variations are possible within the scope ofthe present invention.

When a forward voltage is applied to the pin diode using the upperelectrode 113 and the lower electrode 115, electrons and holes arerecombined in the active layer 105, thereby causing emission of light tooccur. Stimulated emission occurs during a period in which the lightgenerated reciprocates between the upper mirror 107 and the lower mirror103, whereby the intensity of light is amplified. Laser oscillationoccurs when the optical gain exceeds the optical loss, whereby laserlight is emitted perpendicularly to the surface of the semiconductorsubstrate 101 from the opening 116 formed on the upper surface of thecolumn-shaped section 110. The surface of the semiconductor substrate101 is the surface on which the resonator 120 is formed.

Device Fabrication Process

An example of a method of fabricating the surface-emitting laser 400according to the present embodiment is described below with reference toFIGS. 21 to 27. FIGS. 21, 22, and 24 to 27 are cross-sectional views,each schematically showing a step of fabricating the surface-emittinglaser 400 of the present embodiment shown in FIG. 20. FIG. 23 is a planview schematically showing the fabrication step shown in FIG. 22.

The present embodiment illustrates a case of fabricating thesurface-emitting laser 400 using the method of fabricating thesurface-emission type light-emitting device of the first embodiment (seeFIGS. 1 to 8).

The surface-emitting laser 400 of the present embodiment is fabricatedby the following steps (a) to (e).

The step (a) includes forming a multilayer film 150 on the semiconductorsubstrate 101, and etching at least a part of the multilayer film 150,thereby forming the column-shaped section 110 including at least theactive layer 105.

The step (b) includes forming the first matrix applying layer includingthe fillers 160 and a matrix precursor to cover the column-shapedsection 110. In the present embodiment, the matrix precursor is used asthe resin precursor 161 and a case in which the first matrix applyinglayer is used as the first resin layer 417 a will be described.

The step (c) includes forming the second matrix applying layer includingthe fillers 160 and the provisional matrix material by temporarilysolidifying the matrix precursor which make up the first matrix applyinglayer. In other words, the provisional matrix material is formed bytemporarily solidifying the matrix precursor. As a result, the secondmatrix applying layer is formed by the first matrix applying layer. Inthe present embodiment, the second matrix applying layer (second resinlayer 417 b) including the fillers 160 and the provisional matrixmaterial (resin 162) is formed by temporarily solidifying the matrixprecursor (resin precursor 161) which make up the first matrix applyinglayer (first resin layer 417 a). In other words, the resin 162 is formedby temporarily solidifying the resin precursor 161. As a result, thesecond resin layer 417 b is formed by the first resin layer 417 a.

The step (d) includes immersing, for a specific period of time, at leastthe second matrix applying layer (second resin layer 417 b) in theliquid 130 having characteristics which cause the provisional matrixmaterial (resin 162) to be dissolved, thereby removing the second matrixapplying layer (second resin layer 417 b) at least in the area formedover the column-shaped section 110.

The step (e) includes forming the insulating layer 417 which includesthe fillers 160 and covers the side surface of the column-shaped section110 by curing the provisional matrix material (resin 163 in FIG. 27)which makes up the second matrix applying layer (second resin layer 417c).

The step (a) is described below.

The semiconductor multilayer film 150 shown in FIG. 21 is epitaxiallygrown on the surface of the n-type GaAs semiconductor substrate 101shown in FIG. 21 while changing the composition. The semiconductormultilayer film 150 includes the buffer layer 102 formed of n-type GaAs,the lower mirror 103 in which n-type AlAs layers and n-typeAl_(0.15)Ga_(0.85)As layers are applied alternately, the n-type claddinglayer 104 formed of n-type Al_(0.5)Ga_(0.5)As, the active layer 105formed of GaAs well layers and Al_(0.3)Ga_(0.7)As barrier layers havinga multiple quantum well structure in which the well layers are formed ofthree layers, the p-type cladding layer 106 formed ofAl_(0.5)Ga_(0.5)As, the upper mirror 107 in which p-typeAl_(0.85)Ga_(0.15)As layers and p-type Al_(0.15)Ga_(0.85)As layers areapplied alternately, and the contact layer 108 formed of p-type GaAs.The semiconductor multilayer film 150 is formed by depositing theselayers on the semiconductor substrate 101 in that order.

The epitaxial growth temperature is appropriately determined accordingto the type of the semiconductor substrate 101 or the type or thicknessof the semiconductor multilayer film 150. The epitaxial growthtemperature is preferably 600 to 800° C. The period of time needed forthe epitaxial growth is also appropriately determined. As the epitaxialgrowth method, an MOVPE (Metal-Organic Vapor Phase Epitaxy) method, MBE(Molecular Beam Epitaxy) method, or LPE (Liquid Phase Epitaxy) methodmay be used.

A photoresist (not shown) is applied to the contact layer 108 and thenpatterned using photolithography, thereby forming a resist layer (notshown) with a specific pattern. The contact layer 108, upper mirror 107,p-type cladding layer 106, active layer 105, n-type cladding layer 104,and part of the lower mirror 103 are dry-etched using the resist layeras a mask, thereby forming the column-shaped section 110 which is acolumn-shaped semiconductor deposition, as shown in FIGS. 22 and 23. Theresonator 120 including the column-shaped section 110 is formed on thesemiconductor substrate 101 by this step, as shown in FIG. 22.

The step (b) is described below.

In this step, the column-shaped section 110 is covered with the firstresin layer 417 a including the fillers 160 and the resin precursor 161.

A liquid substance containing the fillers 160 and the resin precursor161 (not shown) is applied to the column-shaped section 110 and theupper mirror 103 and then dried, thereby forming the first resin layer417 a to cover the column-shaped section 110, as shown in FIG. 24. Inthis step, the first resin layer 417 a is formed so that the thicknessof the first resin layer 417 a is at least greater than the height ofthe column-shaped section 110, and the column-shaped section 110 iscovered with the first resin layer 417 a. As the fillers 160 and resinprecursor 161, those formed of the materials illustrated in thedescription relating to the structure of the device are used. The resinprecursor 161 is applied after dissolving in a solvent, as required. Inthis case, the solvent is evaporated after the resin precursor isapplied.

As a method of applying the liquid substance, a conventional techniquesuch as a spin coating process, dipping process, or spray coatingprocess may be used. During the application of the liquid substance, itis preferable to prevent unevenness of the film thickness caused by aconvex section formed by the column-shaped section 110 as far aspossible.

The step (c) is described below.

In this step, the resin precursor 161 in the first resin layer 417 a istemporarily solidified by applying energy such as heat or light to theresin precursor 161, thereby forming the second resin layer 417 b, asshown in FIG. 25. For example, the resin precursor 161 is converted intothe resin 162 shown in FIG. 25 by reacting at least a part of the resinprecursor 161 shown in FIG. 24 by irradiation with energy such as heator light. The resin 162 obtained by this step has a lower solubility inthe liquid 130 described later (see FIG. 26) than the resin precursor161. The dose of energy is set so that the resin precursor 161 is notcompletely cured and the fillers 160 are scarcely affected. The secondresin layer 417 b including the fillers 160 and the resin 162 isobtained by this step, as shown in FIG. 25.

This temporarily solidifying step is performed while controlling theperiod of time for applying energy and the dose of the energy dependingon the type or concentration of the resin precursor 161 included in thefirst resin layer 417 a. In the case of temporarily solidifying theresin precursor 161 using heat, the reaction temperature is controlled.In the case of temporarily solidifying the resin precursor 161 usinglight, the amount of light is controlled. In the case of forming theresin 162 (see FIG. 25) having a lower solubility in the liquid 130 thanthe resin precursor 161 by temporarily solidifying at least a part ofthe resin precursor 161 included in the first resin layer 417 a usingheat, the resin precursor 161 is temporarily solidified at a lowertemperature for a shorter period than those employed in a heat curingstep for forming an insulating layer by completely curing the resinprecursor 161. If the dose of the energy applied is insufficient, thesolubility in the liquid 130 is not changed since the resin precursor161 is not fully reacted, whereby the resulting resin is dissolved inthe liquid 130 and removed. If the dose of the energy is too great, thesolubility in the liquid 130 is decreased too much since a large amountof the resin precursor 161 is reacted, whereby the resulting resin isnot dissolved in the liquid 130 and removal of the resin becomesdifficult. Therefore, it is important to control the period of time andthe dose of energy to be applied during temporal solidificationdepending on the type and density of the resin precursor.

As the resin precursor used in this step, a polyimide precursor ispreferably used. The polyimide precursor has a low viscosity andsignificantly shrinks in volume during curing.

As examples of the polyimide precursor, polyamic acid, long-chain alkylester of polyamic acid, and the like can be given. In the case offorming the insulating layer from the polyimide precursor, when thepolyimide precursor is applied and then heated, an imidization reactionoccurs. As a result, a polyimide resin is produced, whereby theinsulating layer is formed. The heating temperature applied when formingthe insulating layer is 150 to 400° C., and preferably 300 to 400° C.,although the temperature is changed depending on type of the polyimideprecursor.

In the case of using a resin cured by irradiation with light as theresin for forming the insulating layer 417 (see FIG. 20), a UV-curablepolyacrylic resin or epoxy resin may be used. Since the UV-curable resincan be cured only by irradiation with ultraviolet rays, problems such aschanges in the device characteristics due to heat can be avoided.

The step (d) is described below.

In this step, a device 400 a obtained by the steps (a) to (c) isimmersed in the liquid 130 for a specific period of time, as shown inFIG. 26. FIG. 26 illustrates a case where the entire area of the device400 a is immersed in the liquid 130. However, it suffices that at leastthe second resin layer 417 b of the device 400 a be immersed.

The liquid 130 has characteristics which cause the second resin layer417 b to be dissolved. The liquid 130 may be appropriately selecteddepending on the type of resin precursor. In the case where the resinprecursor is a polyimide precursor, an alkaline solution may be used asthe liquid 130.

In this step, the solubility of the column-shaped section 110 in theliquid 130 may be lower than the solubility of the resin 162 in theliquid 130. This enables a sufficient margin to be produced relating tothe period of time in which the column-shaped section 110 and the secondresin layer 417 b are immersed in the liquid 130, thereby enablingstable fabrication. Moreover, since the column-shaped section 110 can beprevented from being dissolved in the liquid 130 before the resin 162,effects on the characteristics of the device can be limited.

The solubility of the fillers 160 in the liquid 130 may be lower thanthe solubility of the resin 162 in the liquid 130. This enables thefillers 160 to be prevented from being dissolved in the liquid 130before the resin 162 which makes up the second resin layer 417 b. As aresult, a specific amount of the fillers 160 can be included in theresulting insulating layer 417.

In this step, the second insulating layer 417 c including the fillers160 and the resin 163 is obtained by controlling the period of time andtemperature for immersion in the liquid 130, as shown in FIG. 27. Thesecond insulating layer 417 c is the second resin layer 417 b shown inFIG. 26 of which the area formed over the column-shaped section 110 isremoved, as shown in FIG. 27. In this step, the second resin layer 417 bformed on the lower mirror 103 is also dissolved in the liquid 130. As aresult, the second insulating layer 417 c can be formed so that theupper surface of the second insulating layer 417 c is almost level withthe upper surface of the column-shaped section 110, as shown in FIG. 27.In this step, the fillers 160 present in upper part of the second resinlayer 417 b are removed as the second resin layer 417 b is removed.

The step (e) is described below.

In this step, the insulating layer 417 which covers the side surface ofthe column-shaped section 110 is formed by curing the second resin layer417 c shown in FIG. 27. The second resin layer 417 c is cured at atemperature for a period of time referring to the temperature and periodof time in a conventional step of curing a resin during formation of aninsulating layer. The insulating layer 417 which covers the side surfaceof the column-shaped section 110 is formed by this step, as shown inFIG. 20.

The step of forming the electrodes 113 and 115 for injecting currentinto the active layer 10S is described below.

Before forming the electrodes 113 and 115, the upper surface of thecolumn-shaped section 110 is optionally cleaned using a dry etchingmethod or the like. This enables formation of a device having morestable characteristics. A metal film (not shown) is formed on the uppersurfaces of the insulating layer 417 and the column-shaped section 110using a vacuum deposition process and then annealed, thereby forming analloy layer (not shown) formed of gold, zinc, or the like. The opening116 is formed by patterning the alloy layer using a photolithography.The annealing temperature is usually at about 400° C. The upperelectrode 113 is formed by this step. A metal film (not shown) is formedon the back surface of the semiconductor substrate 101 using a vacuumdeposition process and then annealed, thereby forming the lowerelectrode 115 of an alloy layer formed of gold and germanium, forexample. The surface-emitting laser 400 shown in FIG. 20 is obtained bythe above process.

Action and Effects

The surface-emitting semiconductor laser 400 of the present embodimenthas the following major action and effects. Before describing theseaction and effects, the structure and operation of a commonly-usedsurface-emitting semiconductor laser are briefly described below.

(1) Structure and Operation of Commonly-Used Surface-EmittingSemiconductor Laser

The surface-emitting semiconductor laser is a two-dimensionallyintegratable light-emitting device. Therefore, application of thesurface-emitting semiconductor laser to parallel optical communications,parallel optical arithmetic, and the like as a high-speed,large-capacity light source in the next generation has been expected.The surface-emitting semiconductor laser emits a laser beam from aresonator formed on a semiconductor substrate in the directionperpendicular to the surface of the semiconductor substrate on which theresonator is formed. The resonator functions as a laser oscillator,which is formed by applying a reflection layer, an active layer, and areflection layer in that order.

Current must be injected into the active layer from the surface of thelaser in order to drive the surface-emitting semiconductor laser.Therefore, a pair of electrodes for injecting current into the activelayer is formed in the laser. In order to concentrate the current on theactive layer, a method of forming a section of the resonator includingat least the active layer in the shape of a column using etching isgenerally employed.

(2) Heat is generated in the resonator when driving the surface-emittingsemiconductor laser. This heat increases the temperature near theresonator, whereby the characteristics of the device, in particular,light emission efficiency and maximum output may be decreased. In orderto maintain the characteristics of the device by preventing an increasein the temperature of the device at the time of driving, it ispreferable to cause the heat generated to be efficiently released to theoutside.

In order to insulate the pair of electrodes for injecting current intothe active layer, a method of burying the section formed in the shape ofa column (column-shaped section) in an insulating resin represented by apolyimide is generally employed. However, thermal conductivity of aninsulating layer formed of the insulating resin is generally low.Therefore, if such an insulating layer is formed so that thecolumn-shaped section is buried in the insulating layer, heat generatedat the time of driving may not be released to the outside efficiently,whereby stable characteristics of the device may not be obtained.

On the contrary, according to the surface-emitting laser 400 of thepresent embodiment, the insulating layer 417 includes the fillers 160.The insulating layer 417 is formed using the fillers 160 having aspecific thermal conductivity and coefficient of thermal expansioncorresponding to the thermal conductivity of the semiconductor substrate101 and the coefficient of thermal expansion of the resin 163 whichmakes up the insulating layer 417. This enables the characteristics ofthe insulating layer 417 such as thermal conductivity and coefficient ofthermal expansion to be adjusted. Therefore, strain occurring betweenthe semiconductor substrate 101 and the insulating layer 417 can bedecreased, thereby excellent heat release and good devicecharacteristics can be obtained.

(3) A commonly-used surface-emitting laser is formed by using a GaAssubstrate as the semiconductor substrate and a polyimide resin as theinsulating layer which covers the column-shaped section. In thesurface-emitting laser 400 of the present embodiment, in the case ofusing a GaAs substrate as the semiconductor substrate 101 and apolyimide resin as the resin 163, the insulating layer 417 is formed bycuring the resin precursor at about 400° C. (see fabrication processdescribed later). Heat-curable or photo-curable resins such as apolyimide resin generally have a coefficient of thermal expansiongreater than that of the GaAs substrate which forms the semiconductorsubstrate 101. Therefore, when the device is cooled to room temperatureafter forming the insulating layer 417, a large amount of strain occursbetween the semiconductor substrate 101 and the insulating layer 417 dueto the difference in coefficient of thermal expansion between thesemiconductor substrate 101 and the insulating layer 417. This strainmay cause the semiconductor substrate 101 to be warped or reliability ofthe device to be impaired.

On the contrary, in the surface-emitting laser 400 of the presentembodiment, the fillers 160 included in the insulating layer 417 have afunction of adjusting the difference in coefficient of thermal expansionbetween the semiconductor substrate 101 and the insulating layer 417,whereby the amount of strain can be decreased. In the case of using aGaAs substrate as the semiconductor substrate 101 and a polyimide resinas the resin 163 as described above, the polyimide resin has acoefficient of thermal expansion greater than that of the GaAssubstrate. Therefore, the difference in coefficient of thermal expansionbetween the semiconductor substrate 101 and the insulating layer 417 canbe decreased by allowing the fillers 160 formed of a material having acoefficient of thermal expansion smaller than that of the polyimideresin to be present in the insulating layer 417. As a result, the amountof strain occurring between the semiconductor substrate 101 and theinsulating layer 417 can be decreased, whereby the reliability of thedevice can be maintained. As examples of the material having acoefficient of thermal expansion smaller than that of the polyimideresin, diamond and silicon can be given.

Specifically, the difference in coefficient of thermal expansion betweenthe semiconductor substrate 101 and the insulating layer 417 can bedecreased by allowing the insulating layer 417 to include the fillers160 having a specific coefficient of thermal expansion corresponding tothe difference in coefficient of thermal expansion between thesemiconductor substrate 101 and the insulating layer 417. As a result,the amount of strain occurring between the semiconductor substrate 101and the insulating layer 417 can be decreased.

(4) According to the method of fabricating the surface-emitting laser400 of the present embodiment, effects and advantages the same as thosein the case of using the method of fabricating the surface-emission typelight-emitting device of the first embodiment can be obtained.Specifically, according to the method of fabricating thesurface-emitting laser 400 of the present embodiment, only the secondmatrix applying layer (second resin layer 417 b) in the area over thecolumn-shaped section 110 can be removed without causing damage to thecolumn-shaped section 110 in the step (d) by immersing at least thesecond matrix applying layer (second resin layer 417 b) in the liquid130 for a specific period of time and removing the second matrixapplying layer (second resin layer 417 b) in the area formed over thecolumn-shaped section 110. This enables the device 400 having stablecharacteristics to be obtained. Moreover, the device 400 can befabricated at a lower cost and at high yields.

In the step (c), the provisional matrix material (resin 162) having alower solubility in the liquid 130 than the matrix precursor (resinprecursor 161) is formed by temporarily solidifying the matrix precursor(resin precursor 161) which forms the first matrix applying layer (firstresin layer 417 a). Since the dissolving rate of the provisional matrixmaterial (resin 162) in the liquid 130 is lower than the dissolving rateof the matrix precursor (resin precursor 161) in the liquid 130, amargin during the removal step of the second matrix applying layer(second resin layer 417 b) in the liquid 130 can be increased by thistemporal solidification step.

Moreover, since the greater part of the removed provisional matrixmaterial (resin 162) is dissolved in the liquid 130, the devicecharacteristics scarcely deteriorate due to the provisional matrixmaterial (resin 162) readhering to the device after the removal.

(5) In the fabrication of the surface-emitting laser 400 shown in FIG.20, in the case of forming the insulating layer using a commonly-usedformation step of an insulating layer, an insulating layer having thesame thickness as the insulating layer 417 is formed by applying aninsulating layer (not shown) to cover the column-shaped section 110, andremoving the insulating layer by etching so that the upper surface ofthe column-shaped section 110 is exposed. In this case, the fillers 160included in the insulating layer hinder etching during the etching step,whereby it may become difficult to form the insulating layer at auniform thickness.

On the contrary, according to the method of fabricating thesurface-emitting laser 400 of the present embodiment, the fillers 160present in the upper part of the second matrix applying layer (secondresin layer 417 b) are automatically removed from the second matrixapplying layer (second resin layer 417 b) as the second matrix applyinglayer (second resin layer 417 b) is removed from the upper surface ofthe surface-emitting laser 400 in the step (d). This enables theinsulating layer 417 including the fillers 160 to be formed at a uniformthickness by a step almost the same as a commonly-used formation stepfor an insulating layer.

The above embodiment illustrates the case of a surface-emittingsemiconductor laser having one column-shaped section. However, thepresent invention is not impaired even if a plurality of column-shapedsections is formed on the substrate.

The above embodiment illustrates the surface-emitting semiconductorlaser. However, the present invention is applicable to semiconductordevices other than the surface-emitting semiconductor laser. As examplesof semiconductor devices to which the present invention can be applied,EL devices, LED devices, ICs, piezo devices, and the like can be given.In the case of applying the present invention to ICs, the insulatinglayer including fillers according to the present invention can beapplied to an interlayer dielectric.

Fifth Embodiment

FIG. 28 is a view illustrating an optical module according to a fifthembodiment to which the present invention is applied, and a method offabricating the optical module. The optical module according to thepresent embodiment includes a structure 600 (see FIG. 28). The structure600 includes the surface-emission type light-emitting device 100 of thefirst embodiment (see FIG. 1), a platform 620, a first optical waveguide630, and an actuator 650. The structure 600 also includes a secondoptical waveguide 1302. The second optical waveguide 1302 forms part ofa substrate 1300. A connection optical waveguide 1304 may be opticallyconnected with the second optical waveguide 1302. The connection opticalwaveguide 1304 may be an optical fiber.

In the optical module of the present embodiment, light is emitted fromthe surface-emission type light-emitting device 100 (light exit port116, see FIG. 1), and received by a photodetector (not shown) throughthe first and second optical waveguides 630 and 1302 (and the connectionoptical waveguide 304).

Sixth Embodiment

FIG. 29 is a view illustrating an optical transmission device accordingto a sixth embodiment to which the present invention is applied. In thepresent embodiment, a plurality of third optical waveguides 230, 1310,and 1312 is provided between the first optical waveguide 630 and aphotodetector 210. The optical transmission device according to thepresent embodiment includes a plurality (two) of substrates 1314 and1316.

In the present embodiment, the third optical waveguide 1312 is disposedbetween the structure including the surface-emission type light-emittingdevice 100 (including the surface-emission type light-emitting device100, platform 620, first optical waveguide 630, second optical waveguide1318, and actuator 650) and the structure including the photodetector210 (including the photodetector 210, platform 220, and third opticalwaveguides 230 and 1310). Optical transmission between a plurality ofpieces of electronic equipment can be performed using an optical fiberor the like as the third optical waveguide 1312.

In FIG. 30, an optical transmission device 1100 interconnects with eachpiece of electronic equipment 1102 such as computers, displays, storagedevices, and printers. The electronic equipment 1102 may be informationcommunications equipment. The optical transmission device 1100 includesa cable 1104 including the third optical waveguide 1312 such as anoptical fiber. The optical transmission device 1100 may be one in whichplugs 1106 are provided on both ends of the cable 1104. The structureincluding either light emitting device 100 or photodetector 200 isprovided in each of the plugs 1106. Electrical signals output from onepiece of electronic equipment 1102 are converted into optical signals bythe light-emitting device. The optical signals are transmitted throughthe cable 1104 and converted into electrical signals by thephotodetector. The electrical signals are input to the other piece ofelectronic equipment 1102. According to the optical transmission device1100 of the present embodiment, transmission of information between eachpiece of electronic equipment 1102 can be achieved by optical signals.

FIG. 31 is a view showing conditions of use of an optical transmissiondevice according to the embodiment to which the present invention isapplied. An optical transmission device 1112 interconnects each piece ofelectronic equipment 1110. As examples of the electronic equipment 1110,liquid crystal display monitors or digital CRTs (may be used in thefield of finance, mail order, medical treatment, and education), liquidcrystal projectors, plasma display panels (PDPs), digital TVs, cashregisters (for Point of Sale Scanning (POS)) for retail stores, videocassette recorders, tuners, game machines, printers, and the like can begiven.

In the fifth and the sixth embodiments (see FIGS. 28 to 31), the sameeffects and advantages can be achieved in the case of using thesurface-emission type light-emitting device 200 (see FIG. 9), 300 (seeFIG. 15), or 400 (see FIG. 21) instead of using the surface-emissiontype light-emitting device 100.

Seventh Embodiment

FIG. 32 is a view illustrating an optical transmission device accordingto a seventh embodiment to which the present invention is applied. Thepresent embodiment illustrates a case where the optical transmissiondevice functions as an optical interconnection device 2000 between ICchips as an example.

Device Structure

In the optical interconnection device 2000 of the present embodiment, aplurality of IC chips is formed in layers. The present embodimentillustrates an example in which two IC chips are layered in the opticalinterconnection device 2000, as shown in FIG. 32. However, the number ofIC chips to be layered is not limited thereto.

In the optical interconnection device 2000, laser beams 221 and 222 aretransmitted between layered IC chips 201 and 202 to execute transmissionof data. The IC chips 201 and 202 respectively include substrates(silicon substrates, for example) 211 and 212, and IC regions 401 and402 formed on the substrates 211 and 212. As examples of the IC chips201 and 202, various types of ICs such as a CPU, memory, and ASIC can begiven.

On the IC chip 201, the surface-emitting laser 400 (see fourthembodiment) and a photodetector 301 are disposed on the substrate 211.Similarly, on the IC chip 202 the surface-emitting laser 400 and aphotodetector 302 are disposed on the substrate 212. Thesurface-emitting laser 400 formed on the IC chip 201 is referred to as400X, and the surface-emitting laser 400 formed on the IC chip 202 isreferred to as 400Y.

Device Operation

The operation of the optical interconnection device 2000 is describedbelow with reference to FIG. 32.

In the optical interconnection device 2000, a signal which iselectrically processed in the IC region 401 of the IC chip 201 isconverted into a laser pulse signal by the resonator 120 (see FIG. 20;not shown in FIG. 32) of the surface-emitting laser 400X, and sent tothe photodetector 302 of the IC chip 202. The photodetector 302 convertsthe received laser pulse into an electrical signal and sends theelectrical signal to the IC region 402.

The optical interconnection device 2000 is operated in the same mannerin the case of sending a laser beam from the surface-emitting laser 400Yformed on the IC chip 202 to the photodetector 301. Specifically, in theoptical interconnection device 2000, a signal which is electricallyprocessed in the IC region 402 of the IC chip 202 is converted into alaser pulse signal by the resonator 120 (see FIG. 20; not shown in FIG.32) of the surface-emitting laser 400Y, and sent to the photodetector301 of the IC chip 201. The photodetector 301 converts the receivedlaser pulse signal into an electrical signal and sends the electricalsignal to the IC region 401. In this way, the IC chips 201 and 202transmit data via the laser beam.

In the case where the substrates 211 and 212 consist of siliconsubstrates, light emitted from the surface-emitting lasers 400 isallowed to pass through the substrates (silicon substrates) 211 and 212by setting the oscillation wavelength of the resonators of thesurface-emitting lasers 400 to 1.1 μm or more.

Accompanied by an increase in the processing speed and frequency, thefollowing problems generally occur relating to signal transmissionbetween electrically connected IC chips: occurrence of skew on signaltransmission timing between interconnections; increase in powerconsumption during transmission of a high frequency electrical signal;difficulty of designing interconnection layout; necessity for impedancematching; and necessity for countermeasures to cut off earth noise.

The above problems can be solved by performing signal transmissionbetween IC chips using an optical signal as in the opticalinterconnection device 2000 of the present embodiment.

In the optical interconnection device 2000 of the present embodiment,the surface-emitting lasers 400 are formed on the IC chips 201 and 202.As described in the fourth embodiment, the surface-emitting laser 400includes the column-shaped section 110 and the insulating layer 417which covers the side of the column-shaped section 110, wherein theinsulating layer 417 includes the fillers 160 (see FIG. 20; not shown inFIG. 32). Since heat radiation characteristics of the surface-emittinglaser 400 is increased by this configuration, a stable operation can beachieved.

Specifically, the present invention is not limited to theabove-described embodiments, and various modifications are possible. Forexample, the present invention includes configurations essentially thesame as the configurations described in the embodiments (for example,configurations having the same function, method, and results, orconfigurations having the same object and results). The presentinvention includes configurations in which any unessential part of theconfiguration described in the embodiment is replaced. The presentinvention includes configurations having the same effects or achievingthe same object as the configurations described in the embodiments. Thepresent invention includes configurations in which conventionaltechnology is added to the configurations described in the embodiments.

1. A surface-emitting semiconductor laser including a resonator formedon a semiconductor substrate, which emits light in a directionperpendicular to the semiconductor substrate, comprising: acolumn-shaped section which forms at least a part of the resonator, andan insulating layer which covers a side surface of the column-shapedsection, wherein the insulating layer comprises a filler, wherein thefiller is formed of a material having a coefficient of thermal expansionthat is smaller than a coefficient of thermal expansion of a matrixmaterial which makes up the insulating layer, wherein the filler isformed of at least one of silicon and carbon allotropes includingcarbon, graphite, and diamond.
 2. The surface-emitting semiconductorlaser as defined in claim 1, wherein the thermal conductivity of thefiller is higher than that of the matrix material which forms theinsulating layer.
 3. The surface-emitting semiconductor laser as definedin claim 1, wherein the matrix material which makes up the insulatinglayer is a polyimide resin.
 4. The surface-emitting semiconductor laseras defined in claim 1, wherein the filler is a particle, and thediameter of the particle is smaller than the thickness of the insulatinglayer.
 5. A surface-emitting semiconductor laser including a resonatorformed on a semiconductor substrate, which emits light in a directionperpendicular to the semiconductor substrate, comprising: acolumn-shaped section which forms at least a part of the resonator, andan insulating layer which covers a side surface of the column-shapedsection, wherein the insulating layer comprises a filler, wherein thefiller is formed of a material having a coefficient of thermal expansionbeing smaller than a coefficient of thermal expansion of a matrixmaterial which makes up the insulating layer, wherein the filler is ametal particle having an insulating film on a surface.
 6. Thesurface-emitting semiconductor laser as defined in claim 5, wherein thethermal conductivity of the filler is higher than that of a matrixmaterial which forms the insulative layer.
 7. The surface-emittingsemiconductor laser as defined in claim 5, wherein the matrix materialwhich makes up the insulating layer is a polyimide resin.
 8. Thesurface-emitting semiconductor laser as defined in claim 5, wherein theparticle diameter of the filler is smaller than the thickness of theinsulating layer.
 9. The surface-emitting semiconductor laser as definedin claim 5, wherein the metal particle includes at least one ofaluminum, gold, silver, copper, tin, magnesium, nickel, and zinc as anessential component.